George Zimmerman smiles after a not guilty verdict was handed down in his trial at the Seminole County Courthouse, in Sanford, Fla.

SANFORD, Fla. — After a year and a half of living as a hermit, George Zimmerman emerged from a Florida courthouse a free man, cleared of all charges in the shooting of 17-year-old Trayvon Martin.

His brother said the former neighborhood watch volunteer was still processing the reality that he wouldn’t serve prison time for the killing, which Zimmerman, 29, has maintained was an act of self-defense. Late Saturday night, a jury found him not guilty of second-degree murder and declined to convict him on a lesser charge of manslaughter.

However, with many critics angry over his acquittal, his freedom may be limited.

“He’s going to be looking over his shoulder the rest of his life,” Robert Zimmerman Jr. said during an interview on CNN.

Demonstrators upset with the verdict protested mostly peacefully in Florida, Milwaukee, Washington, Atlanta and other cities overnight and into the early morning Sunday, but some broke windows and vandalized a police squad car in Oakland during protests in four California cities, authorities said. Additional demonstrations were scheduled across the country through Sunday evening.

Churches also made note of the verdict Sunday morning, with many leaders speaking about the case and urging peace in the aftermath. Some congregants wore hooded sweatshirts, as Martin had when he died, or shirts with the teen’s picture.

Martin’s killing in February 2012 unleashed debate across the U.S. over racial profiling, self-defense and equal justice. Protesters nationwide lashed out against police in the Orlando suburb of Sanford as it took 44 days for Zimmerman to be arrested. Many, including Martin’s parents, said Zimmerman had racially profiled the unarmed black teen. Zimmerman identifies himself as Hispanic.

Six anonymous female jurors considered nearly three weeks of often wildly conflicting testimony over who was the aggressor on the rainy night the 17-year-old was shot while walking through the gated townhouse community where he was staying and where Zimmerman lived.

Jurors were sequestered during the trial, and they deliberated more than 15 hours over two days before announcing late Saturday night that they had reached a verdict. The court did not release the racial and ethnic makeup of the jury, but the panel appeared to reporters covering selection to be made up of five white women and a sixth who may be Hispanic.

In August 2012, defense attorney Mark O’Mara said Zimmerman and his wife, Shellie, had been living like hermits and weren’t working because they feared for their safety.

After Saturday’s verdict, police, officials and civil rights leaders urged peace and told protesters not to resort to violence. While defense attorneys said they were thrilled with the outcome, O’Mara suggested Zimmerman’s safety would be an ongoing concern.

“There still is a fringe element that wants revenge,” O’Mara said. “They won’t listen to a verdict of not guilty.”

Those watching reacted strongly when the verdict was announced. Martin’s mother and father were not in the courtroom when it was read; supporters of his family who had gathered outside yelled “No! No!” upon learning of the verdict.

Andrew Perkins, 55, a black resident of Sanford, angrily asked outside the courthouse: “How the hell did they find him not guilty?”

Trayvon Martin’s brother, Jahvaris Fulton, said on Twitter: “Et tu America?” — a reference to the Latin phrase “Et tu, Brute?” known as an expression of betrayal.

In a Sunday afternoon statement, President Barack Obama called Martin’s death a tragedy for America but asked that Americans respect calls for calm reflection.

“I know this case has elicited strong passions,” he said. “And in the wake of the verdict, I know those passions may be running even higher. But we are a nation of laws, and a jury has spoken.”

The statement reflected the widespread national attention of the case. The White House rarely issues formal responses to trials that do not directly involve the president or federal government.

Obama said the verdict should prompt a discussion on gun violence, but it’s unlikely he will use the trial as a way to restart his legislative push for stricter gun control laws. The measures he sought after the December school massacre in Newtown, Conn., failed to pass the Senate.

NAACP President Benjamin Todd Jealous started a petition calling for the Justice Department to open a civil rights case against Zimmerman. “The most fundamental of civil rights — the right to life — was violated the night George Zimmerman stalked and then took the life of Trayvon Martin,” Jealous wrote in the petition, posted on the website MoveOn.org and addressed to Attorney General Eric Holder.

Martin family attorney Benjamin Crump acknowledged the disappointment of Trayvon Martin’s supporters, ranking the teen alongside civil rights heroes Medgar Evers and Emmett Till in the history of the fight for equal justice. However, Crump said, “for Trayvon to rest in peace, we must all be peaceful.”

Martin’s family maintained the teen was not the aggressor, and prosecutors suggested Martin was scared because he was being followed by a stranger. Defense attorneys, however, said Martin knocked Zimmerman down and was slamming the older man’s head against the concrete sidewalk when Zimmerman fired his gun.

Prosecutors called Zimmerman a liar and portrayed him as a “wannabe cop” vigilante who had grown frustrated by break-ins in his neighborhood committed primarily by young black men. Zimmerman assumed Martin was up to no good and took the law into his own hands, prosecutors said.

State Attorney Angela Corey said after the verdict that she believed second-degree murder was the appropriate charge because Zimmerman’s mindset “fit the bill of second-degree murder.”

“We charged what we believed we could prove,” Corey said.

Zimmerman also had some supporters outside the courthouse, including Cindy Lenzen, 50, of Casslebury, and her brother, 52-year-old Chris Bay, who stood watching others chant slogans such as, “the whole system’s guilty.”

Lenzen and Bay — who are white — called the entire case “a tragedy,” especially for Zimmerman.

“It’s a tragedy that he’s going to suffer for the rest of his life,” Bay said. “No one wins either way. This is going to be a recurring nightmare in his mind every night.”

Before a special prosecutor assigned to the case ordered Zimmerman’s arrest, thousands of protesters had gathered in Sanford, Miami, New York and elsewhere, many wearing hoodies like the one Martin had on the night he died. They also carried Skittles and a can of iced tea, items Martin had in his pocket. Obama also had weighed in, saying that if he had a son, “he’d look like Trayvon.”

Despite the racially charged nature of the case, race was barely mentioned at the trial.

“This case has never been about race or the right to bear arms,” Corey said. “We believe this case all along was about boundaries, and George Zimmerman exceeded those boundaries.”

One of the few mentions of race came from witness Rachel Jeantel, the Miami teen who was talking to Martin by phone moments before he was shot. She testified that he described being followed by a “creepy-ass cracker” as he walked through the neighborhood.

Jeantel gave some of the trial’s most riveting testimony. She said she overheard Martin demand, “What are you following me for?” and then yell, “Get off! Get off!” before his cellphone went dead.

The jurors had to sort out clashing testimony from 56 witnesses in all, including police, neighbors, friends and family members.

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Associated Press writers Tamara Lush in Sanford; Kelli Kennedy, Suzette Laboy and David Fischer in Miami; and Julie Pace in Washington contributed to this report.